In a thermal power plant or the like, a fossil fuel is combusted, and therefore a large volume of carbon dioxide (CO2) is generated. With regard to carbon dioxide, as a substance causing warming, control of emissions thereof has advanced in individual countries. As a method for recovering carbon dioxide, a method for absorption thereof using a liquid containing amines such as alkanolamine is currently known as the method closest to practical application (for example, see Patent Literature 1).
A combustion exhaust gas contains, in addition to CO2, and acid gas component such as HCl (hydrogen chloride), NOx (nitrogen oxides), SOx (sulfur oxides) and the like; oxygen, nitrogen, water vapor or the like. If the combustion exhaust gas is brought into contact with CO2 absorption liquid containing amines, not only CO2 but also the acid gas component is absorbed into the CO2 absorption liquid. If the acid gas component is bonded with amines, an inorganic acid salt is formed. For example, hydrochlordie salt is formed from HCl, nitrate is formed from NOx, or sulfate is formed, from SO2. Moreover, if an organic acid, such as formic acid, oxalic acid, acetic acid and the like, which is produced, as a by-product by decomposition of amines, is bonded with amines, an Organic, acid salt is formed. Such an organic facial salt and an inorganic acid salt are a thermally stable salt (hereinafter, referred, to as a heat stable salt in several cases). The heat stable salt causes corrosion of metal or reduction of CO2 absorption capacity. Therefore, the heat stable salt is removed by reclaiming process or the like.
While the CO2 absorption liquid containing amines is used for recovery of carbon dioxide from the combustion exhaust gas, part of amines can be nitrosated in several cases. Moreover, a reclaimer remaining liquid that remains upon converting the heat stable salt in the CO2 absorption liquid in amines by reclaiming process contains the heat stable salt, amines not wholly used for recovery and a nitroso compound produced by nitrosation of amines.
Incidentally, the nitroso compound derived from amines absorbs carbon dioxide in a lower volume than amines of an origin absorb, and reduces carbon dioxide recovery efficiency. Therefore, researches on removing such a nitroso compound have been conducted in various manners. For example, Patent Literature 2 discloses a method for decomposing nitrosamine by irradiating a composition containing the nitrosamine with electromagnetic energy. Moreover, Patent Literature 3 discloses a method comprising heating and decomposing nitrosamine. Most of nitrosamines have a higher boiling point than original amines have. For example, a boiling point of N-nitrosodimethylamine produced by nitrosation of dimethylamine (boiling point: 7.0° C.) is 151 to 154° C., and a boiling point of N-nitrosodiethylamine produced by nitrosation of diethylamine (boiling point: 55.5° C.) is 177° C. A nitrosated compound of amines is required to be heated at high temperature for thermal decomposition. In a method for thermally decomposing the nitrosated compound of amines, amines being a main component in the CO2 absorption liquid are also thermally decomposed together, and therefore loss of amines is large. In a carbon dioxide recovery apparatus in which an ion-exchange resin method or an electrodialysis method is employed, facilities for heating a material at high temperature are not installed, and therefore the facilities for heating the material at high temperature are required for practicing a conventional method for thermally decomposing the nitroso compound. In a carbon dioxide recovery apparatus in which a distillation method is employed for regenerating amines, the nitroso compound contained in the reclaimer remaining liquid discharged from a reclaiming apparatus is required to be treated at low cost.